Objectives of this study are to define the nature and hemostatic functions of factor VIII:C and von Willebrand factor. The primary source of factor VIII is now human material in a collaborative arrangement with Dr. Lars-Olov Andersson of Kabi Biochemicals in Sweden. Our efforts are directed at studying the nature of the factor VIII:C phospholipid interaction and will continue on the purification of factor VIII:C free of von Willebrand factor. The mechanisms of thrombin enhancement of factor VIII:C and the interaction of thrombin activated factor VIII:C with phospholipid will be studied. We also plan to study the interaction of factor VIII and IXa to form the factor X activator.